Methanol, the simplest of the alcohols, is a highly desirable substance which is useful as a fuel, as a solvent, and as a feedstock in the manufacturer of more complex hydrocarbons. In accordance with the method of methanol manufacture that is currently practiced in the petroleum industry, methane is first converted to synthesis gas, a mixture of carbon monoxide and hydrogen. The synthesis gas is then converted over an alumina-based catalyst to methanol. The formation of synthesis gas from methane is an expensive process.
Although often identified as methane, the feedstock for the foregoing synthesis gas process is typically natural gas. As is well known, natural gas often contains significant percentages of sulphur. Since sulphur poisons the catalyst required for its operation, the synthesis gas process for making methanol is further limited by the scarcity of low sulphur natural gas.
As will be apparent, methane and methanol are closely related chemically. Methane comprises a major component of natural gas and is therefore readily available. Despite the advantages inherent in producing methanol directly from methane, no commercially viable system for doing so has heretofore been developed.
The present invention comprises a method of and apparatus for manufacturing methanol from methane or natural gas which overcomes the foregoing and other deficiencies which have long since characterized the prior art. The method involves a gas permeable partition upon which a light-activated catalyst capable of producing hydroxyl radicals from water is deposited, it being understood that as used herein the term "light-activated catalyst" means any catalyst that is activated by electromagnetic radiation regardless of wave length.
Water is present on the catalyst side of the partition and methane or natural gas at positive pressure is present on the opposite side of the partition. The catalyst is exposed to radiation while relative movement is effected between the water and the partition. The radiation-exposed catalyst reacts with the water molecules to form hydroxyl radicals. The gas is forced through the semipermeable partition forming small bubbles in the water. The hydroxyl radicals in the water then undergo a free-radical reaction with the methane in the water to form methanol, and if natural gas is used in the process, ethanol and propanol.
In accordance with the broader aspects of the invention there is generated a stream of sub-micron sized gas bubbles. Due to their extremely small size, the gas bubbles present an extremely large surface area which increases reaction efficiency. Smaller pores in the gas permeable partition facilitate the formation of smaller bubbles. Additionally, higher relative velocity across the partition surface aids in shearing the bubbles off the surface while they are still small.
In accordance with first, second, and third embodiments of the invention, a gas permeable tube has an exterior coating comprising a titanium-based catalyst. The gas permeable tube is positioned within a glass tube and water is caused to continuously flow through the annular space between the two tubes. Methane or natural gas is directed into the interior of the gas permeable tube and is maintained at a pressure high enough to cause gas to pass into the water and prevent the flow of water into the interior of the gas permeable tube. As the water passes over the gas permeable tube, gas bubbles are continually sheared off of its surface. The gas bubbles thus generated are sub-micron in size and therefore present an extremely large surface area.
Electromagnetic radiation generated, for example, by ultraviolet lamps is directed through the glass tube and engages the titanium-based catalyst to generate hydroxyl radicals in the flowing water. The hydroxyl radicals undergo a free-radical reaction with the methane forming methanol, among other free-radical reaction products. Subsequently, the methanol and other products are separated from the reaction mixture by distillation.
In accordance with fourth, fifth, sixth, seventh, and eighth embodiments of the invention, there is provided a hollow disk which supports a gas permeable partition having an exterior coating comprising a titanium-based catalyst. The disk is positioned within a water filled container. Methane or natural gas is directed into the interior of the disk and is maintained at a pressure high enough to cause gas to pass outwardly through the partition and into the water and to prevent the flow of water into the interior of the disk. The disk and the partition are moved at high speed relative to the water. As the gas permeable partition moves relative to the water, gas bubbles are continually sheared off of its surface. The gas bubbles thus generated are sub-micron in size and then therefore present an extremely large surface area.
Electromagnetic radiation generated, for example, by ultraviolet lamps within the container engages the titanium-based catalyst to generate hydroxyl radicals in the water. The hydroxyl radicals undergo a free-radical reaction with the methane forming methanol, and, if natural gas is used in the process, ethanol and propanol. Subsequently, the methanol and other reaction products are separated from the reaction mixture by distillation.
In the practice of the fifth, sixth, seventh, and eighth embodiments of the invention, utilization of the energy comprising the electromagnetic radiation is maximized by providing a mirror within the hollow disk to reflect electromagnetic radiation passing through the porous partition back to the catalytic material. The mirror may comprise either a mirrored surface of the hollow disk or a separate mirror plate. Fluorescent material is utilized to convert broad-band electromagnetic radiation to radiation having a band width which is specific to the selected catalyst. The fluorescent material may be combined with the porous partition, or with the catalytic layer, or may comprise a distinct layer.
In accordance with a ninth embodiment of the invention, a plurality of parallel porous partitions each having a photocatalytic layer on its exterior surface are mounted in an array. The array further comprises sources of electromagnetic radiation positioned between each of the tubular porous partition/photocatalytic layer assemblies. Methane or natural gas from a first manifold is directed into the interior of each of the parallel porous partitions. Water from a second manifold is directed across the surface of the photocatalytic layers in the manner of the first three embodiments of the invention. In addition to activating the photocatalytic layers, energy from the electromagnetic radiation sources generally provides sufficient heat to distill the resulting methanol and higher alcohols from the water.
In accordance with a tenth embodiment of the invention, an oxidizer such as oxygen, peroxide, etc. is mixed with methane or natural gas. The mixture is then directed through a porous partition having a photocatalytic layer on its exterior surface. Water is continuously directed across the exterior surface of the porous partition in the manner of the first nine embodiments of the invention. In this manner the reaction is rendered self-sustaining.